1. Field of the Invention
The present invention relates to an endless transmission belt assembly which may be suitably used for transmitting power between driving and driven pulleys of a continuously variable power transmission mechanism for an automotive vehicle and the like.
2. Description of the Related Art
A typical example of such endless transmission belt assembly is disclosed, e.g., Japanese Utility Model Application Laid-Open Publication No. 53-76844. The known transmission belt assembly in use is passed between driving and driven pulleys of the power transmission mechanism for transmitting power therebetween, of which each pulley is formed with a circumferential belt groove of substantially V-shaped cross-section. The belt assembly is constituted by an endless belt element of a laminated structure formed of a plurality of metal belt layers, and a number of segmentary block elements of substantially V-shaped cross-section to be received in the belt groove of each pulley, and aligned in a longitudinal direction of the belt element.
In the known transmission belt assembly mentioned above, each block element is formed with a belt recess for passing the belt element therethrough with a contact surface which is brought into contact with innermost circumferential surface of the belt element. Each block element is further provided with a rocking edge which comes into contact with an adjacent block element as a relevant span portion of the belt assembly is wound around the pulley, causing a rocking motion of the block element relative to the adjacent block element.
More particularly, when a span portion of the belt assembly is wound around a pulley, each block element is tilted by a predetermined angle with its rocking edge as the tilting axis, following the winding radius of curvature of the belt element. Power is transmitted as each block element undergoes a wedge-contact with opposite walls of the belt groove in the pulley, accompanying contact of adjacent pair of the block elements with each other at the rocking edge. On this occasion, the winding radius of the block element is the radial distance R between the center of the pulley and the rocking edge, and corresponds to the pitch circle radius. Accordingly, assuming the winding radius of the innermost circumferential surface of the belt element to be R.sub.b, and the radial distance between the rocking edge and the contact surface of the belt recess to be h, the radial distance R can be expressed as R=R.sub.b -h. The radial location of the rocking edge and hence of the magnitude of the radial distance between the rocking edge and the contact surface of the belt recess is determined such that each block element is applied with an adequate tilting or rocking moment.
The aforementioned block elements of the conventional transmission belt assembly is constituted solely by a single kind of element of the same size, so that all the block elements are wound around the pulley at a constant time interval. Consequently, the level of peaky noise with a specific frequency component tends to become so high that it causes the user, i.e. driver and/or passengers when the transmission belt assembly is used in a power transmission mechanism of an automotive vehicle, feel uncomfortable.
While there has been a proposal to constitute a belt assembly by means of a plurality of kinds of block elements which are mutually different in width, thereby to disperse the frequency range of the noise and reduce the overall noise level, such a proposal is considered to be disadvantageous from the viewpoint of durability.